Pressure transmission device

ABSTRACT

Pressure transmission tube for medical or veterinary use, adapted to be filled with a liquid substance constituting the pressure transmission medium. Said tube comprises along at least one portion of its length a section having a smaller inner diameter differing from the inner diameter prevailing along the remaining section of its length, which ranges from 0.5 to 2.5 mm, the section of smaller diameter corresponding to a reduction in diameter of the order of 10 to 85 percent.

United States Patent Durand et al. July 8, 1975 {54] PRESSURETRANSMISSION DEVICE 2,667,184 1/1954 Hailer 73/395 2,904,076 9/1959Engelumw... 73/392 [761 lnvenmrs: Dmmdi we Jean James, 2,909,196 10/1959Jeffreys 138/44 9560 Eaub0nfle, Francs; The) 3.128993 4/1964 Plattel38/44 Grand ean, 31 rue Rum I011 3,581,733 6/1971 Grandjean.... 128 205D Lausanne, Switzerland 3,635,089 l/1972 Harding 73/395 2 F] d: 0 t. 101973 I 2] l e c Primary Examiner-Kyle L. Howell [2]] Appl. N0.: 405,049Attorney, Agent, or FirmMichael S. Striker 30 Foreign ApplicationPriority Data 1 ABSTRACT 0m, 11, 1972 Fr e 72 36033 Pressuretransmission tube for medical or veterinary use, adapted to be filledwith a liquid substance c0nsti- [52] 0.5. C1 l28/2.05 D; 73/392; 138/44ing h pre ure transmission medium. Said tube [51] Int. Cl. A61B 5/02mpris along at least one portion of its length a [58] Field of Search128/2, 2 R, 2.05 D, 2105 G, section having a smaller inner diameterdiffering from l28/2.05 R, 2.05 O; 73/392, 395, 420; 138/44 the innerdiameter prevailing along the remaining section of its length, whichranges from 0.5 to 2.5 mm, [5 References Citm the section of smallerdiameter corresponding to a re- UNITED STATES PATENTS duction indiameter of the order of 10 to 85 percent. 1,459,666 6/1923 Adams 73/39211 Claims, 6 Drawing Figures 1 PRESSURE TRANSMISSION DEVICE The presentinvention relates to a pressure transmission tube for medical orveterinary purposes, and also to all apparatus or instruments providedwith such a tube.

The assessment of cardiovascular diseases relies more and more onintra-vascular, intra-cardiac, rachidial, renal and similar pressuremeasurements, apart from the usual clinical clues and the results ofdifferent analyses.

The blood pressure measurement method generally used consists inintroducing a catheter into the cavity to be studied, the lumen of thecatheter being previously filled with an isotonic solution: allvariations in pressure, occuring at the catheter tip are completelytransmitted by the incompressible liquid column filling the catheterlumen. Therefore, the measurement or the recording of the pressurevariations transmitted to the external end of the catheter lumen willdisclose the pressures occurring in the cavity under investigation. Thisis usually achieved by means of a so-called pressure transducer (of theStatham or another type), which provides an electric voltageproportional to the pressure variation.

However, it was found fortuitously that when two catheters of differentdiameters are introduced simultaneously into the same cavity, thepressure curves recorded through each of them, may differ significantlyone from the other. In addition, the necessity of transmitting thepressure signals obtained by means of the catheter to a more or lessdistant electronic device led to interpose a pressure transmission tubebetween the catheter terminal and the pressure transducer. lt was thenobserved that the distortions in the pressure signals was changed butdid not subside.

A careful study of the phenomena led to the following conclusions: likeany solid, fluid, or gazeous body, a catheter designed for transmittingpressure variations as well as the column of liquid filling same has itsown resonance. This resonance arises whenever the hydraulic system,extending from the catheter lumen extremity to the transducer membrane,is stressed anywhere by a mechanical impulse or a pressure change. If noappropriate damping device is provided the pressure variations to bemeasured during their transmission to the transducer undergo significantdistortions caused by the self-resonance phenomena occurring in thecatheter and the pressure transmission tube. The selfresonance frequencyof the most usual catheter lies between and 60 Hz. If the frequency ofthe pressure signals to be measured nears these resonance frequencies,these signals, during their transmission, will undergo an erroneousamplification which may even exceed 400 percent. Even with pressuresignal of much lower frequencies, like those occurring in thecardiovascular system, an erroneous amplification of course lesssignificant, is still observed, but this constitute a cause ofmeasurement errors far from negligible and impossible to estimatebecause appropriate calibration means are not available.

However, in the case of a cardiac catheterization, the mechanicalimpulses imposed to the catheter by the heat and its values, give riseto hydro-mechanical artefacts, often of high amplitude, which interferewith the pressure curves.

The pressure curves which can be recorded during acardiac-catheterization are necessarily altered by the hydromechanicalparasites as well as by the distortion which tends to widen erroneouslythe systolic pressure pulses.

It is the primary object of the present invention to avoid theinconveniences set forth hereinabove by providing an improved pressuretransmission tube easy to use and manufacture, which is to be insertedbetween the catheter and the transducer.

This pressure transmission tube is characterized in that it comprisesalong at least one fraction of its length a section having a smallerinner diameter differring from the inner diameter prevailing along theremaining section of its length, which ranges from 0.5 to 2.5 mm, thesection of smaller diameter corresponding to a reduction in diameter ofthe order of 10 to percent.

Since its inner diameter is not uniform from end to end and comprises atleast one dimensional variation, the tube of this invention has noinherent resonance and is therefore capable of efficiently filtering thepressure signals to be recorded while eliminating the greater part ofthe distortions to which these signals are exposed during theirtransmission. In fact, it is known that the flow of liquids, thepropagation of a pressure and the production of resonance waves in tubesof relatively small diameter constitute complex phenomena accordinginter alia to the laws of Reynolds and Hagen- Poiseuille; therefore, theresonance or damping frequencies depend on the tube length and moreparticularly on the fourth power of the inner diameter of this tube. Thecharacteristics of the catheter selected by a practicioner for a giveninvestigation cannot be modifled; therefore, the resonance frequenciesshould be eliminated in the pressure transmission tube by resorting to asequence of pipe sections having mutually shifted resonance frequencies.

According to a first form of embodiment of the pressure transmissiontube of this invention the tube has an inner diameter of constant value,except in a section of smaller inner diameter which consists of a neckhaving a relatively reduced length, within the range of 5 to 50mm, thisneck being positioned in the first third of the total length of the pipesystem, adjacent the end connected to the member or apparatus fordetecting the pressure to be transmitted, for example a catheter.

In a modified form of embodiment the pressure transmission tube of thisinvention comprises the end to end assembly of at least two separatetube or pipe sections having inner diameters of different values, onesection having an inner diameter within the range of 0.5 to 2.5 mm, theother section having a small inner diameter, the reduction in diametercorresponding to 10 to 85 percent of the inner diameter of said onesection. Besides, the length of the pipe having the smaller innerdiameter is equal to or less than the three-fourths of the total lengthof the tube assembly.

The attached drawing illustrates by way of example typical embodimentsof the device of this invention. In the drawings:

FIG. 1 is a side clevational view ofa first embodiment of a pressuretransmission tube according to this invention;

H6. 2 is a fragmentary axial section of this tube;

H6. 3 is a cross-section taken along the line lll-lll of FIG. 2;

FIG. 4 is a side elevational view of another embodiment wherein the tubeconsists of a pair of pipe sections of different diameter, disposed endto end;

FIG. is a fragmentary axial section of this tube, and

FIG. 6 is a cross-section taken along the line VI-VI of FIG. 5.

In the example illustrated in FIGS. 1-3 of the drawing the pressuretransmission tube according to this invention comprises a single tubesection 1 of a length of 50 to 300 cm. The inner diameter of this tubeis within the range of 0.5 to 2.5 mm.

Advantageously, this tube consists of plastic material such aspolyethylene. polyamide, P.V.C., E.V.A., etc. At one end, this tubecarries a connector 2 for connecting the tube to a catheter adapted tobe introduced into cavities of a patient or an animal for measuringpressures therein. At its opposite end this tube comprises anotherconnector for connecting the tube to a transducer or a measuringinstrument.

According to this invention, this tube comprises a neck or constrictedportion 3 where at its inner diameter is reduced by about to about 85percent. If for instance the inner diameter of the tube is 1.5 mm, theinner diameter at this neck portion is reduced to 0.6 mm The length ofthis neck portion is extremely small and lies within the range of 5mm to50mm. It will be noted that this neck portion is located in the firstthird of the length of tube 1, adjacent the connector 2 for connectingsame to a catheter.

As illustrating in FIGS. 2 and 3, the neck portion 3 may advantageouslybe obtained by fitting an external tubular insert 4 to the tube 1 andshrinking this insert by means of a suitable shrinking machine. Thistubular insert 4 may consist of stainless steel, copper or aluminium.

In the form of embodiment illustrated in FIGS. 4-6 the pressuretransmission tube of this invention consists of a pair of pipe sectionshaving different inner diameters, which are assembled to each other atone end, i.e. a first section la having an inner diameter within therange of 0.5 to 2.5 mm and a second section lb having an inner diameterreduced by 10 to 85 percent with respect to the inner diameter of saidfirst section 10. At this end opposite to the second tube section lb thefirst tube section la carries a connector 2 for connecting the tube to acatheter. 0n the other hand, the free end of the second tube section lbcarries another connector for connecting the assembly to a transducer orother measuring instrument. Possibly, the first section la may comprisea neck 30 similar to the neck 3 of the first embodiment shown in FIGS.1-3.

The two tube sections In and lb are assembled by means of a connectorshown generally at 5.

This connector 5 comprises a metal tube 6 having an evolutive innerdiameter corresponding exactly on the one hand to the inner diameter oftube section 1a and on the other hand to the inner diameter of tubesection lb, for it is essential in devices of this character to avoidany unevennesses likely to retain air bubbles, how small they are. Thistube 6, like tube 4, may consist of stainless steel, aluminium or othersuitable material. Finally, the reference numeral 8 designates a socketobtained by moulding a suitable elastomer over the ends of tubes la andlb, on the one hand, and connecting tube 6, the function of this socket6 consisting simply of reinforcing this joint between tube sections laand lb of the pressure transmission tube and thus prevent any accidentalrupture at this location.

First Application 5 The problem consisted in making a 130 cm longpressure transmission tube to be connected to a conventional catheter, asocalled Cournands catheter" No. 5, F-SW, having a length of 125 cm andan inner diameter of 0.66 mm. The pressure transmission tube havingequal resonance frequencies, has been obtained by joining end to end, afirst 100 cm long tube, having an inner diameter of 0.5 mm, with asecond 30 cm long tube, having an inner diameter of 1.2 mm. These tubesections are connected as shown at 5, FIG. 5. However, it is not deemednecessary to describe in detail the connectors fitted to the ends of theconnecting tube, since they are manufactured by conventional methodswell known to all catheter manufacturers.

Second application The problem consisted in making a I50 cm longpressure transmission tube, to be connected to a 125 cm long catheterFlexo-Pulmocath No. 13, having an inner diameter of 0.90 mm. Thepressure transmission tube was according to the invention, comprised oftwo polyamide tube sections joined end to end: the first section was 100cm long and had an inner diameter of 0.5 mm; the second section was 50cm long, and had an inner diameter of 1.3 mm.

Third application The problem consisted in making a I80 cm long pressuretransmission tube, to be connected to a I25 cm long catheter"Flexo-Pulmocath No. 13, having an inner diameter of 0.90 mm.

The pressure transmission tube according to the invention consistedoftwo tube sections joined end to end: the first section was 90 cm longand had an inner diameter of0.5 mm, the second section was 90 cm longand had an inner diameter of L2 mm.

In actual practice, with due regard for the resonance frequencies of thecatheter in general use having an inner diameters of 0.5 to 2.0 mm, thetubes or tube sections constituting the pressure transmission tubeaccording to the invention may have an inner diameter from 0.5 to 2.0mm; however the inner diameters and lengths of these tube sections mustbe selected as a function of the catheters to be equipped with dueconsideration for the above mentioned laws.

The device according to this invention, can be used whenever it iscontemplated, to observe or record a pressure existing in a cavity, forinstance, the bloodpressure, the intra-cardiac pressure, theintra-vascular pressure, the intra-cerebral pressure, the renalpressure, the amniotic cavity pressure, the intra-rachidial pressure,the peritioneal cavity pressure, etc. This device can be used in themedical and the verterinary arts, as well as in all laboratories, forany kind of researches.

However, its specific application consists in recording theintra-vascular and the intra-cardiac blood pressure. Of course, thepresent invention also included all pressure transmission tubes, alsoreferred to as connecting tubes, having different inner diameters,having or not constricted ,or widened sections which, when joined end toend, permit of obtaining a composite tube having a non-uniform innerdiameter.

The present invention may also include pressure transmission tubes madeof tube sections of which the cross-sectional contour is not a circlebut any other configuration.

The present invention may also include a pressure transmission tube.made from a tubular element having a variable or evolutive innerdiameter; this result can be obtained, during the actual manufacture, byusing an extruder having movable punch and die members.

What we claim is:

1. In a device for use in measuring blood characteristics, particularlyblood pressure or the like, having a catheter tube for insertion intothe blood stream of a body and a transducer apparatus for picking up andconverting pressure variations into proportional electrical voltagevariations susceptible of measurement, a combination comprising apressure transmission tube having two spaced end portions and adapted tobe filled with a substantially immobile liquid pressure transmissionmedium, said end portions respectively communicating with said cathetertube and said transducer, and said pressure transmission tube definingan internal passage free of turbulence-producing projections andcomposed of at least two communicating main sections, one of said mainsections having a constant inner diameter of between 0.5 and 2.5 mm andhaving a first self-resonant frequency, and the other of said mainsections having a second self-resonant frequency and being of narrowerdiameter than said one main section and having a constant inner diameterof between through 85 percent of said inner diameter of said one mainsection, whereby the self-resonant frequencies of said catheter tube andsaid pressure transmission tube are shifted away from the frequencies ofthe pressure variation signals to be measured so as to provide errorfreemeasurement of the latter; and joining means forming a continuousinternal channel located intermediate said sections of said pressuretransmission tube and communicating with said internal passage so as toaccommodate said liquid medium therein in a nonturbulent manner.

2. A device as defined in claim 1, wherein said one main section iscomposed of at least two spaced portions and the other of said mainsections is located intermediate said two portionsv 3. A device asdefined in claim 2, wherein the other of said main sections is the firstthird of the total length of said pressure-transmission tube as measuredfrom that one of said spaced end portions which communicates with saidcatheter.

4. A device as defined in claim 1; and further comprising constrictionmeans for contricting said pressure-transmission tube, said constrictionmeans being a tubular sleeve located externally of saidpressuretransmission tube and surrounding the same, said sleeve being ofa shrinkable material and being shrunk to said tube, so as to therebyconstrict the latter to attain said inner diameter of the other of saidmain sections.

5. A device as defined in claim 1, wherein the other of said mainsections adjoins said one main section.

6. A device as defined in claim 5, wherein the other of said mainsections has a length which is less than three-fourth of the totallength of said pressuretransmission tube.

7. A device as defined in claim 5, wherein the other of said mainsections has a length which is equal to three-fourths of the totallength of said pressuretransmission tube.

8. A device as defined in claim 5, wherein the length of each of saidmain sections is between 30 cm and [50 cm; and wherein said innerdiameter of one of said main sections is between 1.0 and 1.5 mm., andsaid inner diameter of the other of said main sections is between 0.3and 0.8 mm.

9. A device as defined in claim 1; and further comprising support meansfor supporting said joining means.

10. A device as defined in claim 9, wherein said internal channel ofsaid joining means evolutively communicates with said main sections ofsaid pressure transmission tube.

I]. A device as defined in claim 1; and further comprising connectormeans located at each of said spaced end portions for respectivelyconnecting said pressure transmission tube to said catheter and saidtransducer.

1. In a device for use in measuring blood characteristics, particularlyblood pressure or the like, having a catheter tube for insertion intothe blood stream of a body and a transducer apparatus for picking up andconverting pressure variations into proportional electrical voltagevariations susceptible of measurement, a combination comprising apressure transmission tube having two spaced end portions and adapted tobe filled with a substantially immobile liquid pressure transmissionmedium, said end portions respectively communicating with said cathetertube and said transducer, and said pressure transmission tube definingan internal passaGe free of turbulence-producing projections andcomposed of at least two communicating main sections, one of said mainsections having a constant inner diameter of between 0.5 and 2.5 mm andhaving a first selfresonant frequency, and the other of said mainsections having a second self-resonant frequency and being of narrowerdiameter than said one main section and having a constant inner diameterof between 10 through 85 percent of said inner diameter of said one mainsection, whereby the self-resonant frequencies of said catheter tube andsaid pressure transmission tube are shifted away from the frequencies ofthe pressure variation signals to be measured so as to provideerror-free measurement of the latter; and joining means forming acontinuous internal channel located intermediate said sections of saidpressure transmission tube and communicating with said internal passageso as to accommodate said liquid medium therein in a non-turbulentmanner.
 2. A device as defined in claim 1, wherein said one main sectionis composed of at least two spaced portions and the other of said mainsections is located intermediate said two portions.
 3. A device asdefined in claim 2, wherein the other of said main sections is the firstthird of the total length of said pressure-transmission tube as measuredfrom that one of said spaced end portions which communicates with saidcatheter.
 4. A device as defined in claim 1; and further comprisingconstriction means for contricting said pressure-transmission tube, saidconstriction means being a tubular sleeve located externally of saidpressure-transmission tube and surrounding the same, said sleeve beingof a shrinkable material and being shrunk to said tube, so as to therebyconstrict the latter to attain said inner diameter of the other of saidmain sections.
 5. A device as defined in claim 1, wherein the other ofsaid main sections adjoins said one main section.
 6. A device as definedin claim 5, wherein the other of said main sections has a length whichis less than three-fourth of the total length of saidpressure-transmission tube.
 7. A device as defined in claim 5, whereinthe other of said main sections has a length which is equal tothree-fourths of the total length of said pressure-transmission tube. 8.A device as defined in claim 5, wherein the length of each of said mainsections is between 30 cm and 150 cm; and wherein said inner diameter ofone of said main sections is between 1.0 and 1.5 mm., and said innerdiameter of the other of said main sections is between 0.3 and 0.8 mm.9. A device as defined in claim 1; and further comprising support meansfor supporting said joining means.
 10. A device as defined in claim 9,wherein said internal channel of said joining means evolutivelycommunicates with said main sections of said pressure transmission tube.11. A device as defined in claim 1; and further comprising connectormeans located at each of said spaced end portions for respectivelyconnecting said pressure-transmission tube to said catheter and saidtransducer.